In recent years, progresses in diagnostic imaging techniques, such as MRI, have provided various findings. Based on these findings, it has been pointed out that a clear correspondence is not necessarily present between the frequent occurrence of cerebral infarction and dementia, and that Binswanger type cerebral infarction and leuko-ariosis correspond closely with symptoms of dementia. Furthermore, clinical investigations in our country have resulted in reports of many cases in which microvascular lesions without apoplectic stroke progress, leading to dementia (Akiguchi et al., 1995). The reports have indicated that not only in Binswanger type cerebral infarction, but also in the brains of elderly people, removal of the white matter, compared with the gray matter, is marked, and the loss of myelins, in particular, is severe. These reports suggest the possibility that many of diseases, generally categorized as cerebrovascular dementia, may be dementia due to demyelination. Myelin is a marrow sheath formed by the plasma membrane of oligodendrocytes (oligodendroglia cells) surrounding the axon. Because of demyelination, which primarily impairs this myelin sheath, the accuracy and the transmission speed of impulses propagated through the axons decline. This decline is presumed to cause higher function disorder, such as amnesia, or dyskinesia. As demyelination progresses, the nerve cells themselves degenerate and fall off. Thus, it is important to activate oligodendrocytes, which form the myelin sheath and support the nerve cells, in order to maintain the function of the nerve cells. Conventional therapies, which activate only nerve cells, cannot be expected to restore the function impaired by demyelinating disease.
Such demyelinating diseases showing dementia are becoming serious problems at the present time when society is rapidly aging. Development is hastily under way for therapeutic pharmaceuticals which are intended to prevent and treat these diseases and which act on oligodendrocytes by mechanisms different from the conventional therapies. The object of the present invention is, therefore, to provide a preventive and therapeutic pharmaceutical effective for the prevention and treatment of various diseases associated with demyelination.